Conventional zoom devices require coupled mechanical motions to adjust the axial separations between individual or group elements in order to change the optical magnification as disclosed in U.S. Pat. No. 3,970,367 to Tsuji, U.S. Pat. No. 3,975,089 to Betensky, U.S. Pat. No. 4,097,124 to Watanabe, and U.S. Pat. No. 4,189,213 to Iizuka.
FIG. 1 illustrates a conventional mechanical zoom system. At the very basic level, a zoom system includes at least one moving lens for zooming. One lens or group of lenses to change the image size is called the variator 11 and another lens or group or lenses to maintain focus throughout the zoom range is called the compensator 12. The variator 11 is moved to change the image size of an object. However, the image is defocused because the imaging position is also changed while the variator changes the image size of the object. Therefore, the variator 12 must move in unison with the compensator lens 12 to zoom and keep the image 13 in-focus. These movements are usually mechanically controlled by a zoom ring on the lens barrel.
The mechanical motions decrease the speed of zooming, increase space and weight as well as the power consumption and possibly induce of unwanted jitter. In addition, the mechanical zoom system is restricted to magnifying the area on-axis.
U.S. Pat. No. 4,407,567 to Michelet discloses a zoom device comprising piezoelectric multilayer structures. This system requires a high voltage, a large structure, a high manufacturing and maintenance cost, which make it difficult to implement in the small portable devices such as camera phone, PDA, portable computer, etc.
U.S. Pat. No. 4,190,330 to Berreman discloses a variable focus system comprising a nematic liquid crystal material. Its focal length is changed by modulating the refractive index. It has a slow response time typically on the order of hundreds of milliseconds. Even though the fastest response liquid crystal lens has the response time of tens of milliseconds, it has small focal length variation and low focusing efficiency.
Therefore, there has been a need for a small and fast zoom device that can change magnification.